The invention relates to a temperature sensing device that is portable and can accurately sense temperature conditions and actuate an indicator in response to such sensing. The invention is particularly useful with appliances such as freezers, refrigerators, coolers, and the like. Should the temperature in the storage area of such appliances rise above a certain value, damage to products stored therein can result.
The device according to the present invention is capable of accurately sensing when the temperature in a volume to which the device of the invention is operatively connected rises above a predetermined value, the device according to the invention being accurate to 3 percent in sensing the relevant temperature. Because of its portability, the device according to the invention is extremely versatile and can be quickly and easily disposed in operative association with the appliance to be protected. Preferably the device provides an audible alarm which can be easily heard.
The device according to the present invention includes a voltage measurement bridge which in a simple and inexpensive manner accurately facilitates sensing of the temperature in the volume occupied by a temperature probe operatively associated with the device, and actuates an indicator in response thereto. The temperature probe comprises a component part of the voltage measurement bridge, and one of the resistors in the voltage measurement bridge is a variable resistor which is readily adjustable to set the alarm-initiating temperature. In practice, the variable resistor is adjustable so that the relevant temperature may be adjusted from about zero to about 50.degree. F. This also facilitates versatility of the device, providing appropriate protection for freezers, refrigerators, beverage coolers, vegetable storage areas, and the like.
The device according to the present invention includes circuitry means for detecting when the probe is not operatively connected to the device, for whatever reason, such as when the probe is damaged, severed from the main unit, or is simply pulled out of the protected appliance. The missing probe detection circuitry means is simple and effective, eliminating hysteresis feedback, and providing a minimum number of component parts.
It is the primary object of the present invention to provide a simple, effective, efficient, and versatile device for sensing temperature conditions above a predetermined adjustable value. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.